Sanitary napkins in use suffer from two major disfunctions. One of these is leakage. In most instances, leakage results not from saturation of the absorbent material, but rather fluid run off from the surface of the porous fluid permeable cover material prior to the penetration of the fluid through the cover and into the absorbent matrix. This may be due to a variety of factors, such as the nature of the fluid itself. Menses is a complex fluid which may be highly viscous and contains amongst other components cellular debris and a mucoidal fraction. Both the mucoidal fraction and the cellular debris tend to collect at the surface capillaries of the cover material and block the transmission of the more aqueous component into the absorbent.
Difficulties in this downward fluid transmission is heightened by the irregular capillary size and shape and even areas of complete lack of capillaries which can occur in the manufacturing processes associated with certain nonwovens. Fluid therefore strikes the surface of the cover and is blocked or the downward transmission retarded. Fluid then tends to spread along the surface and over the side edges resulting in napkin failure even though the bulk of the absorbent layer at either end, of the napkin has not even been wet. The other dysfunction which has only recently been identified relates to wetness of the cover. Because tabless sanitary napkins are designed to be attached to tight fitting undergarments, the surface of the nonwoven cover material is in direct contact with the perineal area, because of the tight fitting undergarments used by the wearer. Since the nonwoven cover materials are inherently nonwettable, there is a wet or damp surface feeling associated with them even when there is adequate downward transmission.
Attempts have been made to increase comfort of tabless sanitary napkins as well as to insure greater surface contact in the perineal area by providing napkins with inwardly arcuate sides. These napkins supposedly conform to the shape of the thighs adjacent the perineal area and therefore will suffer less distortion from movement by the wearer and it is theorized provide better fluid transmission downward into the absorbent component and due to the better surface interface between the perineal area and the cover.
In another type of sanitary garment, i.e., diapers, there is generally not the intimate contact between the crotch of the wearer and the containment garment. Diapers are, of course, of a vastly different configuration. Diapers, even though they include a fluid pervious nonwoven cover, an absorbent and a fluid impermeable baffle, are designed to be an undergarment with complete encircling of the legs and waist. Side leakage is prevented in diapers by the utilization of elastic completely around the leg area to provide a seal. U.S. Pat. No. 4,326,528 discloses a diaper which is arcuate in cross-sectional profile and constructed to form a containment pocket. U.S. Pat. No. 4,226,238 describes a rather complicated diaper construction in which a slightly elasticized central pouch is formed. U.S. Pat. No. 3,371,668 describes a sanitary napkin which utilizes elastic for certain constructional purposes. This type of seal is impossible to be obtained with a sanitary napkin which is not designed to be a garment with encircling means around the leg openings. European Pat. No. 0091412 discloses a sanitary napkin with elasticized edges, which due to its construction, features a raised bulky central area and side flaps.